Jupiter and Saturn shine brightly at opposition as the Tears fall

Alan Pickup

Author: Alan Pickup
The maps show the sky at midnight BST on the 1st, 23:00 on the 16th and 22:00 on the 31st.

To the welcome relief of astronomers at our northern latitudes, August brings the return of truly dark skies just in time for the peak of the annual Perseids meteor shower, once called the Tears of St Lawrence. We also have the oppositions of Jupiter and Saturn, which, being opposite the Sun, are at their brightest and best as they cross our night sky from the south-east at sunset to the south-west at dawn.

Standing high on the meridian at our map times is the Summer Triangle, though stretched from side-to-side by the map’s projection. The bright stars Vega in Lyra, Deneb in Cygnus and Altair in Aquila, mark its corners but its expanse includes a wealth of interesting objects and the two other minor constellations, Sagitta the Arrow and Vulpecula the Fox.

Albireo, Mark Phillips

The brightest of these, Sagitta, is the third smallest of all the constellations in the sky, lying 10° north of Altair and just below Vulpecula. Another 10° northwards, and slightly west, is Albireo, the beak of Cygnus the Swan and one of the showpiece double stars in the sky with contrasting gold and blue components. We may glimpse them through binoculars, but a telescope shows them at their striking best.

The Milky Way arches through the Triangle on its way from Sagittarius on the south-south-west horizon to the bright star Capella in Auriga around 15° high in the north-north-east. Halfway between Capella and the “W” formed by the brighter stars of Cassiopeia, higher in the north-east, is the place in Perseus from which Perseids appear to radiate.

The shower’s meteors, though, appear in all parts of the sky and are already arriving as they build to a peak on the 12th before petering out by the 24th. Plenty of swift meteors, many leaving glowing streaks or trains in their wake, are seen near the maximum, with numbers predicted to exceed 80 per hour for an observer under perfect conditions. Given the absence of bright moonlight, this could be a bumper year for Perseids-spotting.

The shower’s meteoroids originate with Comet Swift-Tuttle which was discovered in 1862 and takes 133 years to orbit the Sun. Records of the shower, however, date back over two millennia while its whimsical name as the Tears of St Lawrence may have a macabre origin in early Christian tradition. The saint was martyred on August 10, AD258, some say by being roasted alive over an iron grill – with the not unconnected consequence that he is now regarded as the patron saint of chefs.

The Sun sinks 10° southwards during August as Edinburgh’s sunrise/sunset times change from 05:17/21:20 BST on the 1st to 06:15/20:09 on the 31st. Its decline also draws the curtain on the season for viewing those high-level noctilucent clouds that I have highlighted in recent notes.

Crescent Moon, Fran Goodman

The Moon is new on the 8th, at first quarter on the15th, full on the 22nd and at last quarter on the 30th. Its path against the stars takes it low across our southern sky at our star map times from Libra, low in the west-south-west, on the 15th and through the Teapot of Sagittarius, low in the south, on the 18th. It reaches full phase in Capricornus on the 21st and on that evening stands 7° below and right of the conspicuous planet Jupiter in the south-south-east.

The Moon’s progress carries it below the Square of Pegasus in the east and onwards to lie 11° right of the Pleiades in the east-north-east on the 28th. The star cluster heralds the return of the spectacular and familiar constellations that light up our winter nights and by the time our August nights end Orion is in full view in the east-south-east.

Jupiter surpasses every star as it comes to opposition on the 20th when it lies 600 million km away, shines at magnitude -2.9 and shows a cloud-banded disk though a telescope. Climbing to stand almost 21° high on Edinburgh’s meridian about two and a half hours after our map times, it creeps 4° eastwards during the month to cross the border from Aquarius to Capricornus.

Ganymede shadow transit, Mark Phillips

Binoculars, held steadily or preferably on a tripod, allow us to glimpse the four brighter Jovian moons which circle above the Jovian equator in “months” as short as 1.8 Earth-days for the inner one, Io, and 16.7 days for the outermost, Callisto. Telescopes, even small ones, show them more easily and allow us the track their motion across Jupiter’s cloudy disk, or watch them disappear behind it. We may also spy the inky black shadows that the moons can cast onto the clouds and there are even, this month, a few instances when one moon eclipses another.

Jupiter has another 75 moons, mostly small bodies less than 5 km wide and discovered by professional astronomers using large telescopes or during spacecraft flybys. Earlier in July, though, the amateur astronomer Kai Ly claimed to have discovered another moon, Jupiter’s 80th, after sifting through years of official survey images of Jupiter and its environs. Unless the claim is overruled by the professional community, this appears to be the first moon of any planet to be discovered by an amateur.

Saturn and 5 moons, Radim Stano

Saturn reaches opposition on Monday when it lies 1,337 million km distant and shines as a magnitude 0.2 object on Capricornus where it is also edging westwards. It lies 18° to the right of Jupiter, passes 5° lower across the meridian, and stands 5° above the Moon on the 20th. Its rings, spanning 42 arcseconds around Saturn’s 19 arcseconds globe, make it an unmissable telescopic beauty.

Venus is probably the only other planet visible in Scottish skies though its altitude in the west to west-south-west at sunset sinks from 8° to 6° and it sets less than one hour later. Brilliant at magnitude -4.0, it lies 6° below-right of the young 12%-illuminated Moon on the 11th. Mercury and Mars hide in the twilight below and to the right of Venus.

Diary for 2021 August

Times are BST

  • 1st 15h Mercury in superior conjunction on far side of Sun
  • 2nd 07h Saturn at opposition at distance of 1,337m km
  • 2nd 08h Moon 5° S of Pleiades
  • 3rd 08h Moon 6° N of Aldebaran
  • 6th 21h Moon 3° S of Pollux
  • 8th 15h New moon
  • 11th 08h Moon 4° N of Venus
  • 12th 20h Peak of Perseids meteor shower
  • 13th 11h Moon 6° N of Spica
  • 15th 16h First quarter
  • 16th 20h Moon 4° N of Antares
  • 20th 01h Jupiter at opposition at distance of 600m km
  • 20th 23h Moon 4° S of Saturn
  • 22nd 06h Moon 4° S of Jupiter
  • 22nd 13h Full moon
  • 25th 01h Summer solstice on Mars
  • 29th 16h Moon 5° S of Pleiades
  • 30th 08h Last quarter
  • 30th 16h Moon 6° N of Aldebaran

This is an extended version, with added diary, of Alan’s article published in The Scotsman on July 31 2021, with thanks to the newspaper for permission to republish here.